Paul Walker death: Celebrities react, investigation continues

Paul Walker's death on Saturday afternoon in a fiery car crash drew reactions from his famous costars and other celebs, and a makeshift memorial grew at the site of the Santa Clarita wreck.

The "Fast and Furious" star, 40, was killed when the 2005 Porsche Carrera GT he was a passenger in hit a tree and a concrete lamp post, exploding into flames. The driver, Walker's friend and business partner Roger Rodas, also died. The sound of the crash was audible from the car shop where Walker and others had gathered earlier in the day for a charity event, a witness told L.A. Now.

Law enforcement was still investigating how fast the car might have been going and whether drag racing might have played a role; an update was not expected until Monday. Meanwhile, people close to the Always Evolving shop -- co-owned by the actor and Rodas -- wondered to TMZ whether an automotive malfunction, specifically a steering issue, might have occurred.

"Fast" costar Tyrese Gibson, who broke down in tears at the crash site on Saturday, leaving a flower at the memorial, remembered his friend in a post on Instagram in which he wrote, "My heart is hurting so bad no one can make me believe this is real Father God I pray that you send clarity over this cause I just don't understand My heart hurts it's broken no one can convince me that this is real.... Prayer warriors please pray real hard for his only child, his daughter and family... #HeartOfAnAngel13YrsFamilyForeverWeJustCelebreatedYour40thBirthday..... My God... My God... I can't believe I'm writing this."

Other costars were similarly broken-hearted over the actor, who'd also appeared in films including "She's All That," "Pleasantville" and the upcoming "Hours."

"Your humble spirit was felt from the start," Ludacris wrote. "Wherever you blessed your presence you always left a mark, we were like brothers & our birthdays are only 1 day apart, now You will forever hold a place in all of our hearts@paulwalker legacy will live on forever. R.I.P."

For more celebrity reactions, click through the photo gallery at the top of this post.